1. Field of the Invention
The invention relates to an injection-molding machine for plastic with a screw that is located in an injection cylinder. By means of a single electric motor, the screw is moved by a mechanical rotary drive, which is connected to the drive shaft of the screw, and by a linear drive. The linear drive is connected by a piston-cylinder unit, which is moved by a pressure medium pump connected to the electric motor.
2. Discussion of the Prior Art
A drive arrangement, especially for injection-molding machines, is known from German reference DD 135 876. This arrangement has a shared variable-speed electric motor, which drives the plasticizing screw directly via a clutch or clutches of additional power-transmitting machine elements. At the same time the motor is flanged to the drive shaft of the hydraulic pumps of the electric motor, in order to drive the pressure flow user.
Another injection-molding machine for plastic is known from German reference DE 39 37 099. This machine has a shared electric driving motor that causes the screw to rotate as the plastic granulate is plasticized. The driving motor then presses the injection unit in the direction of the discharge opening by the distance of the injection stroke. The rotary drive and the injection unit are connected by a variable-speed transmission to a driving motor shared by both. To permit execution of the linear movement after the rotary movement, a clutch is provided in the transmission. The clutch disconnects the pressure medium pump from the driving motor.
In the known injection-molding machines for plastic, it is disadvantageous that the transmission sometimes continues to operate during the operation of the driving motor. In addition, the pump in an open hydraulic circuit can be driven only in one direction.